The invention relates to a method for marking data of a digital data stream representing video or audio information.
In bitstream recording one is free to subdivide the bitstream into sub-units of more regular structure. Presentation data in DVDs (digital video or versatile disc) is organized into units called Video Object Unit, denoted VOBU, e.g. in the DVD Specifications for Video Recording. VOBUs have a variable size (data amount measured in number of sectors), but have also a variable duration (measured in number of video fields).
For data retrieval from the disc the DVD Specifications for Video Recording foresees a xe2x80x98VOBU mapxe2x80x99 which is a table where for every VOBU in a recording the length in sectors and the duration in fields is entered.
It is one object of the invention to disclose a method for marking digital data as being temporarily erased in such a way, that on the fly permanent erasure can be achieved without any additional view into the streams.
According to the invention, this object is achieved by means of the features specified in main claims. Advantageous designs and developments are specified in subclaims.
The directory and file structure of DVD Stream Recording is organized in Stream Data and Navigation Data of the DVD Stream Recording as follows:
Any DVD Streamer Device has certain requirements to store its own, Streamer-specific navigation data on the disc. These data are solely for helping the retrieval of recorded data; they need not be understood or even be visible to any outside Application Device.
Any DVD Streamer Device needs to communicate with the Application Device it is connected to. This communication should be straightforward, and as universal as possible, so that the maximum possible range of applicationsxe2x80x94both today and futurexe2x80x94can be connected to the Streamer. The Navigation Data to support such communication must be understandable by the Streamer as well as by the Application Device; they will be called xe2x80x9cCommon navigation dataxe2x80x9d in the following.
The Streamer Device should offer to the connected Application Device a means for storing its own private data of any desired kind. The Streamer needs not to understand any of the content, internal structure, or meaning of this xe2x80x9cApplication-specific navigation dataxe2x80x9d.
Navigation data is provided to control the recording, playing back, and editing of any bitstreams that are recorded. In DVD Stream Recording, Navigation Data is called xe2x80x9cStreamer Informationxe2x80x9d (STRI). STRI consists of six kinds of information tables, namely Streamer Video Manager Information (STR_VMGI), Stream File Information Table (SFIT), Original Program Chain Information (ORG_PGCI), User Defined Program Chain Information (UD_PGCI), Text Data Manager (TXT_DT_MG), and Application Private Data Manager (APD_MG).
The Stream File Information Table contains the information where on the recording media the stream data are recorded. The Original PGC Information has the function of a play list, which contains all takes which were made. A take is defined as containing the information between a start and a stop action in the sequence of recording or also called one program of the ORG_PGCI. In addition, a Stream Object (SOB) contains a full take or part of a take. With both tables the data can be retrieved for playback.
The User Defined PGC Information contains information, which are defined by a user.
In order to address more precisely a program contains one or more cells. A cell points to Stream Object Units (SOBU) and to each SOBU an Incremental Application Packet Arrival Time (IAPAT) is assigned.
According to the invention besides a temporarily erased flag TE two offset values are introduced in order to indicate a SOBU, which can be erased completely for storing additional information.
In order to exactly address the SOBUs, which can be completely erased the two offset values (TE_S_OFF and TE_E_OFF) shall be added to the Cell Type (C_TY) flag. The exact location of these SOBUs is given by a Stream Cell Start Application Packet Arrival Time (SC_S_APAT), Stream Cell End APAT (SC_E_APAT), a mapping list (MAPL) and these two additional offsets TE_S_OFF, TE_E_OFF. For example the calculation of the start of the first temporarily erased SOBU starts with a coarse location via SC_S_APAT and the MAPL. The search via the MAPL results in 2 possible positions of the assigned SOBU, e. g. SOBU #m or SOBU #m+1. In order to define exactly, whether SC_S_APAT is the first application packet of a SOBU or not the offset value TE_S_OFF contains the needed additional offset with values 0, 1 or 2 to locate the desired SOBU relative to the coarse result of the search via the MAPL.
According to the invention the structure of the C_TY byte is as follows: